Effect of p H on the Activity of Erythromycin Against 500 Isolates of Gram-Negative Bacilli

Abstract

Erythromycin was found to be a more effective inhibitor of gram-negative bacilli in alkaline medium than in neutral or acid medium. A definite effect was noted with all of 500 recent clinical isolates of Escherichia coli, Klebsiella-Enterobacter, Pseudomonas aeruginosa , and Proteus mirabilis studied, but it was most striking with E. coli . At p H 8.5 all strains, except for 14% of those of P. mirabilis , were inhibited by concentrations of erythromycin readily achieved in urine with common therapeutic doses.